Plastic process



Patented Apr. 22, 1930' uNrrED [STATES PATENT oFF-rcE WILLIS A. BOUGHTON, OF CAMBRIDGE, MASSACHUSETTS, ASSIGNOR TO BENNETT BOX COMPANY, OF BOSTON, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS PLASTIC No Drawing.

This invention relates to improvements in plastic processes. More particularly it relates to processes for dealing with sheets of stiflening material suitable for use for toe boxes for shoes, althoughit is applicable for dealing with other materials which it may be desired to transmute between a firm state and a plastic or workable state.

In the ordinary commercial processes of making toe boxes it is customary to soften the material, for the lasting operation, by the addition of heat or by dipping the material into a solvent. There are objections to both of these processes. When heat is used, the softening must be executed always at least twice, just before slipping into the toe for pulling over and again when the toe is last- 'ed or wiped in to produce an even smooth it providesa means for softening without,

either heating or dissolving the stiffening material. veloped in connection with toe boxes for shoes, the improved stifiening material disclosed herein and the methods for dealing with stifi materials may be used for other v purposes so far as they are suitable.

The invention is illustrated as it may be applied to stifi'eningrnaterials, usually organic, such as pitch or rosin which are ordinarily softened by heat, or such as celluloid or any cellulose ester which areordinarily softened by a solvent. liquid. The

softening is efiected by the action of a volatile liquid, upon whose evaporation the stiff condition recurs; and the evaporation may be arranged to occur sufficiently slowly and under suitable conditions to favor the recovcry of the liquid.

Softeners provided by the invention work Although the invention has been de-' 1 PROCESS Application filed January 7, 1925. Serial No. 1,037.

on the following principle: To a volatile liquid in which the organic stiffener is soluble, or to a mixture of liquids if preferred, is added another volatile liquid or mixture which is soluble or miscible in the first in all proportions, but in which the organic stiffener is insoluble. hicle, as it were, for'other liquids of either type whose presence may be desired for various purposes, or may be controlled in its action by the addition of comparatively nonvolatile liquid to alter the volatility of the resulting mixtures or to alter the solvent power, or rate of action, or for other effects. The working liquid having been prepared according to the needs of the operation inhand and results desired, the stifi'ener material, when immersed in it, gradually becomes soft, the softness progressing from the surface inward, until the whole is non-resiliently flexible, somewhat like a cloth wet with water. Nevertheless the stiffener does not leave the felt or other support on which it is carried and enter the liquid. That is, it does not dissolve in the ordinary sense. Even when suspended for hours in the softening liquid no stiffener is lost in solution, if the proportions of solvent to non-solvent are correct, and in the absence of high boiling or-molecularly dispersing solvents of certain kinds. When such a softened box sheet is squeezed, some of the softened stiffener may indeed stick to the fingers, if the concentration of solvent is great enough, but when in a pile each sheet may be separated" from its neighbors without undue sticking. When the softened box is removed from the working liquid. and exposed to the air or to any drying medium it loses the working liquid by evaporation or other process, and when dry is found hardened to approximately original condition. This occurs with such a slow time factor that the softness continues, after removal from the liquid bath, during an ample period in which the lasting may be carried out in an efficient manner, notwithstanding the delays which occur in passing material from one operation to another in ordinary factory I practice. The box thus softened lasts in the This. mixture may be a vepends on various specific conditions of operation, composition of softening liquid, th1ckness of stifiened sheet, temperature, etc. The resulting box has been found to be in every way as good as those produced from similar stiffening material by the commonly practiced processes of heating and in some ways better than such. In addition it is to be ob served that the process is cleanly; that the material remains soft long enough to be used on shoe making processes that cannot use the heating method, such as the turn-shoe rocess; and that the method appears to pro uce a smoother toe than the old process. The absence of heat removes danger to the leather; the process is cheaper to operate than those using heat; and the box itself cheaper to make. And it is not necessary to use a highly inflammable liquid.

An illustrative example of the practice of the-invention follows: A sheet of suitable supporting material is first saturated with an organic stiffener of any desired or suitable sort, which may for example comprise melted rosin, or a mixture of gums, or celluloid or any cellulose ester. The supporting means may consist of loosely. matted cellulose such as paper stock, kraft or sulfite pulp, re-pulped newspaper stock, or felt or cloth; and in case the stiffening material be such as not to need these supporting sheets, as in the case of some celluloid stiifeners, the supporting sheet may be omitted. The prepared sheet is then cut with a die into the suitable form for the toe box, known sometimes as a disc, and may be skived. For the purposes of the present illustrative example it may be assumed that the stiffener is made of rosin, with dye if desired. Using a supporting sheet of repulped material 7 0 mils thick preferably including a thin cloth reinforcement or support, and saturated with rosin applied in molten form, the excess of stifiener liquid may be squeezed out by rolling between heated rollers. Then if desired the pulp may be further compressed to 50 mils by rerolling the cold saturated sheets between hot rolls. This molten composition thus having been impregnated into a suitable supporting sheet, and cooled to solid and stiff form, the prepared sheet can be shipped to market or otherwise may await its .use in the-shoe. When they are to be used, such sheets can be died to shape; can be skived satisfactorily; and may then be immersed in a softening liquid which in the present example may contain'approximately 30 to 35 parts by volume of denatured alcohol No. 1 (a mixture of 90% ethyl alcohol and 10% methanol) mixed with 70-to parts of water. The stiff sheet may become soft enough to last in the toe of a shoe within half an hour to five hours, depending on several controllable variables such as temperature, thickness of sheet, etc.

The lasting is easily performed. The operator does not need to hurry his work, the operation is clean and not smeary, and the quality of the leather is not in danger of being injured. The last may be withdrawn after three hours; and the toe is hard enough to be worn after one to three days. The drying may be accomplished in an enclosure so that the solvent liquid is recovered to be used over and over again. The approximate proportion of the constituents must however be maintained, by occasional observation and addition of fresh material as may be needed from time to time, especially if careful effort is not made to recover the solvent liquid as fully as possible.

If some tackiness of the box is desired, in order that it may adhere to the doubler, leather or lining of the shoe, this can easily be secured by using a greater concentration or proportion of the dissolving component of the mixed liquid. Should a softer box he required, this may be produced by adding to the softening liquid a portion of comparatively non-volatile solvent for the stiflener. One half per cent of such a liquid as xylene or toluene will produce a toe which is notably more flexible. Such a toe holds the shape of the last, but because it tends to soften under the heat of the foot, it will'easily conform to the shape of the foot, which is an advantage that may be desired by some as it markedly decreases the discomfort which is ordinarily attendant upon the breaking in of new shoes.

By incorporation of gum of various qualities and proportions in the stiffener the characteristic of the stiffened material may be considerably altered. In particular a composition can be chosen whose melting or softening point, under heat, is safely higher than that of the composition at present commonly used in those processes in which the softening for lasting is effected by heating, in which the softening temperature is often so low that in the finished shoe the toe loses its shapeif the wearer accidentally rests it close to a steam pi e. Should a permanently softer material be desired it can be obtained by substituting in part a non-drying oil, such as castor oil or cotton seed oil, or a drying oil such as linseed or tung oil, or by some combination of constituents of a gummy or waxy nature.

This process is also well adapted to the soft ening of sheets of cloth, felt, etc. used for other urposes, stiflened with the said types of sti ening material, and is not necessarily confined either to shoe boxes or to materials using pulp.

T am unable to explain at the presenttime the exact nature of the physico-chemical process by which this type of mixed liquid acts as a softener and not as a solvent, but it seems ossible (on the principle that if liquid A is soluble in liquid B, then liquid B must be soluble to some extent in liquid A) that when the stiffener is placed in contact with the mixed liquid it acts as a solvent for that consemi-fluid mixture, until it reaches an equilibrium in which the non-solvent has as much attraction for this solvent liquid as the stiffener has. At that point no more enters, or

' atleast as much leaves as enters; and the presence in the mixed liquid of a constituent in which the stiffener .is insoluble prevents any (or at least prevents all except a very little) of the stiffener from passing into the liquid. It is evident that the softening of-the stifi'ener or other solid results from some degree of absorption of the solvent into its own mass because with use the liquid becomes weaker in the solvent and its strength can be restored by adding more of the solvent. And the going of the stiffener into solution in the liquid is negatived by the absence of discoloration of the liquid. I

The purpose of having the liquid volatile is to make the operation complete within a commercially desirable period of time. The

volatile liquid that dissolves the stiffener may be any suitable solvent, therefore, such as alcohol, acetone, or any mixture of these, or other solvent. The non-dissolving volatile liquid or mixture of liquids, which acts as a restrainer, is one in which the stiffener is insoluble but which mixes with the first liquid,

- and preferably one which mixes in all proportions with it. For arosin or celluloid stiffener, water isa useful example of a suitable restraining liquid. In the illustration above given a practical test for telling the proper proportions is to observe whether the liquid ecomes discolored, which indicates that the rosin is passing into solution, and calls for a larger proportion of the restraining liquid in making the stifl'ener soft, if it be desired that it should not become tacky or sticky or be wasted.

If tacki'ness be desired, another method is to di the sdftened box into purer solvent just each of which may add its peculiar effect tothe mixture. Xylene and other coal tar solvents, for example roduce a tackiness as well as a softenin t is also to be observed that by the addition of solids (either inorganic salts or organic material) which go into solution, the solution may produce other specific desirable ,eflects, among which may be a dyeing of the stiffener.

For a stiffener of different type the softening mixture must be selected differently in accordance with the principles stated. Thus, where the stiffener is a gelatin or glue, the softening liquid may have water as its dissolving agent and a suitable inorganic liquid in which the glue does not dissolve, but which mixes with or dissolves in the water, as the restraining agent. To this may-be added formaldehyde to toughen the glue and render it resistant to water. Potassium bichromate also will tend to render the glue insoluble in water after being lasted in the shoe. 4

For a specific example of softening a stiffened sheet of the type last mentioned, a piece" of glue-coated buckram may be immersed in a mixture of 25 parts of water which is the solvent liquid and parts of acetone which is the non-solvent liquid. In one such instance this was found to soften within an hour anda half to a flexibility like that of wet sail canvas, that is to limpness; and the glue did not dissolve off upon continued soaking in the same liquid for twentyfour hours; and upon the removal and drying of the coated buckram thereafter it again became hard and stiff.

In the practice of the invention it appears that the fibers of the supporting material such as cloth aid materially in the efiect of the solvent. This is indicated by the fact that a pure rosin mixture after many hours immersion in thesoftening liquid described for rosin shows marked softening of the surface, but not penetration throughout, the softening extending beneath to a depth of about 0.2 to 0.3 millimeters. But where the rosin is carried on a supporting material the entrance of the li uid through the fibers aids the penetration of the solvent to interior surfaces of the stiffening material with consequent softening in the interior of the mass as well as at its surface. Rapidity of softening will be influenced by the closeness of fibers to one another and by the corresponding thinness of layer of rosin around each fiber.

In the appended claims the single term alcohol is used in order to avoid the use of alternative phraseology, but it will be understood that this is not so restrictive in meaning as to exclude derivatives or other substances which are equivalents of alcohol, of which manyare known.

I claim as my invention:

1. A method of preparing stiffener blanks for use in shoes and the like, comprising the steps of impregnating a carrier sheet with melted rosin, ermitti the rosin to harden to a stiff condition, an thereafter, prior to reshaping the stiffener blank in a shoe or other article, introducing said blankinto a liquid mixture consisting of 30 to 35 per cent by volume of solvent and 70 to 65 per cent of non-solvent, and capable of softening the 1 stifiener blank Without substantial dissolution during immersion of the blank in the liquid mixture for hours.

2. A method of preparing stiffener blanks for use in'shoes and the like, comprising the m steps of impregnating a carrier sheet with stifiening material, permitting the stifiening material to harden to a stifi condition, and thereaftenprior to reshaping the stiffener blank in a shoe or other article, introducing said'blank into a liquid mixture consisting of to per cent by volume of alcohol and 70 to per cent of Water and capable of softening the stifiener blank Without substantial dissolution (luring immersion of the blank in g; the liquid mixture for hours.

Signed at Boston, Massachusetts, this sixteenth day ofDecember, 1924.

W I!v A. BGUGHTON. 

